The exemplary embodiments are directed to a system, method and device for measuring toner adhesion and adhesion distribution among particles of a toner sample.
The xerographic process relies on the transfer of charged toner particles from one surface to another by way of an applied electric field. A base (toner) particle is a composite material generally made by melt-mixing a polymer resin with an appropriate pigment, along with optional charge control agent, gel additive and other processing aids, followed by extrusion, pulverization and classification to produce the base toner particle of a certain size. Toner is then made by blending the base particles with surface additives such as silica particles and titania particles to control the flow and charge of the final toner. Sometimes optionally zinc stearate, PTFE particles, CeO particles or blade lubricant additive Uadd can be used to aid the performance of the final toner in a given printing system. The toner particles may be irregular or substantially spherical in shape depending on the manufacturing process.
More recently, chemical processes, such as suspension polymerization and emulsion aggregation (EA) processes, are used to manufacture the base (toner) particles. These base toner particles are substantially more spherical. Surface additives may then be blended onto the surface of the base toner particles as described above. The theoretical amount of surface area that is covered by the surface additives can be calculated based on the size of the base toner particles and the size of the additive particles. The term 100% SAC (surface area coverage) denotes the state where the entire surface of the toner particle is covered with additive, theoretically.
Generally, the performance of the toner, e.g., flow, improves as the amount of additive increases or as SAC increases. In the other words, there is a minimum amount of surface area coverage for optimal performance. In toner manufacturing, the SAC is usually set above the minimum value to ensure high toner performance latitude in the machine and robust manufacturing. Even with this precaution, due to human error, raw material sourcing problems, or blending machine issue, additives sometimes may not be blended as well as needed for the process designed. In such a case, even though the SAC is above the minimal value, the additive is not distributed uniformly as designed and this results in toner particles with inferior performance or off the performance specification.
Today, this performance shortfall can only be revealed by system test in machine. At the time of the machine test, large quantities of toner have already been made. This off-spec batch of toner will have to be discarded or recycled, thus wasting time and money. A simpler method for detecting this kind of shortfall prior to the machine test is needed. The essence of the xerographic process lies in the manipulation of toner particles through the print engine, from the development subsystem to the photoreceptor to paper and then fusing. Toner adhesion plays a critical role in this toner marking process. The ability of knowing the adhesion of the toner in terms of the actual value and its distribution would be crucial in predicting its performance in machine.
A number of toner adhesion measurement techniques, such as electric field detachment (“e-field detachment”), ultra-centrifugation, and atomic force microscopy (“AFM”) have been reported. E-field detachment emulates development at a mag brush and electrostatic transfer at the transfer nip. B-field detachment only measures electrostatic adhesion force and the measurement only determines the average adhesion of many toner particles, not the distribution of adhesion within the toner sample. The technique is similar to xerography.
The centrifugal detachment technique measures detachment of toner particles by centrifugal force. This technique aids in determining the average adhesion of many toner particles, but not distribution thereof. The centrifugal detachment technique measures electrostatic as well as Van der Waals forces for a batch of toner particles. The measurement provides an average adhesion for a toner sample, but not the distribution of adhesion. Specifically, there are many toner particles within a toner sample. The centrifugal detachment technique determines the average adhesion even though the actual adhesion of each toner particle is different; and there exists a distribution of adhesion among the many toner particles.
Atomic force microscopy is used to determine adhesion force by measuring the Van der Waals forces of a single toner particle. However, the technique is limited in that only a single particle is measured, one area at a time, and thus statistical data is difficult to obtain. Atomic force microscopy directly measures the adhesion force between a toner particle and a substrate.
The above-discussed techniques measure adhesion, but not distribution of adhesion in a given sample of toner particles. For every toner sample, there may be thousands of toner particles. While distributions of toner size, shape and charge are known, very little is known about the distribution of adhesion within a toner sample. There is also very little information about the uniformity of adhesion within a toner particle.
The above-discussed techniques yield data in the form of a percent of toner detached during e-field detachment; a percent of toner removed during centrifugal detachment; or adhesion force in the case of atomic force microscopy, but only for a single toner particle, one contact area in each measurement.